Method of forming a semiconductor device

ABSTRACT

A method of forming a semiconductor device includes forming a first well and a second well in a substrate, wherein the first well is doped with dopants of a first conductivity type and the second well is doped with dopants of a second conductivity type. A third well is formed within the first well, and a gate structure is formed above the substrate, the gate structure partially overlying at least the first and second wells. A first epi region is formed on the third well, wherein the first epi region is doped with second dopants of the second conductivity type, and a drain region is formed that is electrically coupled to the second well.

BACKGROUND 1. Field of the Disclosure

The present disclosure relates to semiconductor devices and to a methodof forming semiconductor devices, and, more particularly, to fieldeffect transistors in fully depleted silicon-on-insulator technologiesat advanced technology nodes, such as 22 nm and beyond.

2. Description of the Related Art

In recent years, lateral double-diffused MOS transistors (LDMOSFETs)have been increasingly applied in high voltage and smart powerapplications. The advantages over vertical double-diffused MOSFETs(VDMOSFETs) are a reduction in the number of application steps, multipleoutput capability on the same chip, and compatibility with advanced verylarge scale integration (VLSI) technologies. LDMOSFETs with VLSIprocesses are expected to drive ICs to wider fields of complexapplications, such as intelligent power ICs. Actually, with the internetof things (IoT) or internet of everything becoming a term that is moreand more popular, IoT promises a vast field of application in medical,automotive, industrial, metrology, fitness and more applications. Thesedifferent applications largely have several requirements in common, suchas cost sensitivity, long battery life, and increasingly wirelessconnectivity. Particularly, the latter requirement of wirelessconnectivity demands wireless interfaces requiring radio frequency (RF).Recently, a process at 28 nm targeting at IoT in mobile applications hasbeen proposed, this process adding RF modeling to high-K metal gate(HKMG) processes, being designed for devices that require those standbypower and long battery life integrated with RF/wireless functionality.

Generally, LDMOSFETs implement an asymmetric structure with a driftregion located between the LDMOSFET's channel and drain contact. Withregard to FIG. 1a , a schematic cross-section of an LDMOSFET 100 a inaccordance with bulk technologies is schematically illustrated. TheLDMOSFET 100 a comprises a bulk substrate 110 a having a first well 112a and a second well 114 a formed in an upper surface portion of the bulksubstrate 110 a. The first well 112 a and the second well 114 a aredoped with dopants of opposite conductivity types, i.e., P-type andN-type dopants. Overlying an interface between the first well 112 a andthe second well 114 a, a gate electrode 120 a is disposed over the bulksubstrate 110 a, the gate structure 120 a partially covering the uppersurface regions of the first well 112 a and the second well 114 a. Thegate structure 120 a has a gate stack 122 a comprising a gate dielectric(not illustrated) and a gate electrode material (not illustrated). Theperson skilled in the art will appreciate that the gate dielectric andthe gate electrode material, though not explicitly illustrated in FIG.1a , are formed in accordance with known gate formation techniques, andsidewalls of the gate stack 122 a are covered with a sidewall spacer 124a. A source region 132 a is provided within the first well 112 a inalignment with the gate structure 120 a, wherein a lateral distancebetween the source region 132 a and the gate stack 122 a is adjusted bymeans of the sidewall spacer 124 a.

As illustrated in FIG. 1a , a drain region 134 a is formed within thesecond well 114 a. The drain region 134 a is substantially doped withdopants of the same conductivity type as the second well 114 a. Aconcentration of dopants of the second conductivity type within thedrain region 134 a is substantially higher than a concentration ofdopants of the second conductivity type within the second well 114 a.For example, in order to implement an NLDMOSFET, the source and drainregions 132 a and 134 a are strongly doped with N-type dopants, i.e.,the source and drain regions 132 a, 134 a are N+ regions. The first well112 a is doped with P-type dopants implementing a P-well, while thesecond well 114 a is doped with N-type dopants for forming an N-well.

With regard to FIG. 1a , extension regions and halo regions may beprovided within the first well 112 a, as indicated by reference numeral136 a, for adjusting the threshold voltage of the LDMOSFET 100 a. Thegate electrode 120 a covers the surface of the channel within the firstwell 112 a and the drift region within the second well 114 a. The driftregion within the second well 114 a being covered by the gate structure120 a extends into a long drift region indicating a spacing between thegate structure 120 a and the drain region 134 a. Accordingly, theLDMOSFET as illustrated in FIG. 1a has three major serial resistancecomponents in accordance with the channel region in the first well 112 abelow the gate structure 120 a, the drift region within the second well114 a below the gate structure 120 a, and the long drift region withinthe second well 114 a extending beyond the gate structure 120 a to thedrain region 134 a. For LDMOSFETs in high voltage applications, thedominant part among these serial resistance components is given by thedrift region within the second well 114 a below the gate structure 120 aand the long drift region within the second well 114 a beyond the gatestructure 120 a to the drain region 134 a. Accordingly, for LDMOSFETs inhigh voltage applications, the dominant part among these serialresistance components is the drift resistance provided by the driftregion and the long drift region, receiving the high voltage drop alongthe LDMOSFET 100 a.

As illustrated in FIG. 1a , a back bias contact region 138 a is formedwithin the first well 112 a, the back bias contact region 138 a beingenclosed by STI regions 142 a, 144 a separating the back bias contactregion 138 a and the source region 132 a. The back bias contact region138 a is doped with dopants of the same conductivity type as the firstwell 112 a, having a higher concentration of dopants than the first well112 a. Accordingly, the back bias contact region 138 a represents ahighly doped region 138 a within the first well 112 a.

With regard to FIG. 1b , an LDMOSFET 100 b is schematically illustratedin a cross-sectional view, the LDMOSFET 100 b being formed in accordancewith a pure slave FDSOI semiconductor device construction. The term“pure slave” indicates that the LDMOSFET 100 b uses technologycomponents, mostly implants, which are already required for by otherbaseline devices and, therefore, the LDMOSFET 100 b is integrated inaccordance with processes employed in the baseline for formingsemiconductor devices at 28 nm and above. Particularly, the LDMOSFET 100b is not formed by dedicated process features and, therefore, does notrequire additional mask layers in the process flow.

Although the LDMOSFET 100 b is formed in accordance with FDSOItechniques, the LDMOSFET 100 b is provided in and above a bulk substrate110 b which is part of an SOT substrate (the term “silicon-on-insulator”or “SOT” indicating a substrate configuration having an activesemiconductor layer which is separated from a bulk substrate below bymeans of an interposed buried oxide (BOX) layer). Particularly, theLDMOSFET 100 b is formed within a bulk exposed region of the SOTsubstrate, that is, a local region of the SOT substrate (notillustrated), where the active semiconductor layer (not illustrated) andthe BOX layer (not illustrated) are locally removed to locally expose anupper surface of the underlying bulk substrate 110 b. For example, bulkexposed regions or BULEX regions may be formed when implementing backbias in FDSOI technologies, wherein back bias contacts regions areformed adjacent to VDMOSFETs, the back bias contacts being electricallycoupled to the BULEX regions.

With regard to FIG. 1b , the bulk substrate 110 b has a first well 112 band a second well 114 b formed in an upper surface portion of the bulksubstrate 110 b. The first well 112 b and the second well 114 b aredoped with dopants of opposite conductivity types, i.e., P-type andN-type dopants. Overlying an interface between the first well 112 b andthe second well 114 b, a gate electrode 120 b is disposed over the bulksubstrate 110 b, the gate structure 120 b partially covering the uppersurface regions of the first well 112 b and the second well 114 b.Similar to the gate structure 120 a, the gate structure 120 b has a gatestack 122 b comprising a gate dielectric (not illustrated) and a gateelectrode material (not illustrated). The person skilled in the art willappreciate that the gate dielectric and the gate electrode material,though not explicitly illustrated in FIG. 1b , are formed in accordancewith known gate formation techniques, and sidewalls of the gate stack122 b are covered with a sidewall spacer 124 b.

A source region 132 b is provided on the first well 112 b in alignmentwith the gate structure 120 b, wherein a lateral distance between thesource region 132 b and the gate stack 122 b is adjusted by means of thesidewall spacer 124 b. As opposed to the LDMOSFET 100 a, the sourceregion 132 b is formed by an epitaxially grown region which is inalignment with the gate stack 122 b.

Furthermore, a drain region 134 b is formed on the second well 114 b.The drain region 134 b is substantially doped with dopants of the sameconductivity type as the second well 114 b. A concentration of dopantsof the second conductivity type within the drain region 134 b issubstantially higher than a concentration of dopants of the secondconductivity type within the second well 114 b. The drain region 134 bis, as the source region 132 b, an epitaxially grown region, which maybe formed when growing the source region 132 b.

Similar to the description of FIG. 1a above, an NLDMOSFET may beimplemented by the source region 132 b and the drain region 134 b beingstrongly doped with N-type dopants, i.e., the source region 132 b andthe drain region 134 b are N+ regions. In case the first well 112 b isdoped with P-type dopants implementing a P-well, the second well 114 bis doped with N-type dopants for forming an N-well.

Similar to FIG. 1a above, a back bias contact region 138 b is formedwithin the first well 112 b, the back bias contact region 138 b beinglaterally enclosed by STI regions 142 b, 144 b separating the back biascontact region 138 b and the source region 132 b. The back bias contactregion 138 b is doped with dopants of the same conductivity type as thefirst well 112 b, having a higher concentration of dopants than thefirst well 112 b. The back bias contact region 138 b represents a highlydoped region 138 b formed on the first well 112 b as an epitaxiallygrown region. An STI region 146 b separates the drain region 134 b andthe gate structure 120 b.

FIG. 1b shows a direct port of an LDMOS design of bulk technologies toFDSOI technologies, that is, the fabrication of LDMOSFET devices asdescribed above with regard to FIG. 1a is directly transferred intoFDSOI process flows as pure slave LDMOS devices.

Irrespective of the type of LDMOSFET, that is, the LDMOSFET 100 a or theLDMOSFET 100 b, the integration of pure slave LDMOSFETs makes extensiveuse of logic device construction elements, such as forming well regionsin the device body, forming of complementary well regions for the draindrift region and the formation of source/drain regions, either byimplanting the source/drain regions or epitaxially growing source/drainregions.

The major difference in LDMOSFET 100 b with respect to LDMOSFET 100 a,however, is the absence of extension and halo regions, because they arenot required for baseline SOI devices. It turns out that, upon employingbulk and FDSOI techniques in slave LDMOS process flows, body/drainextension implants (wells 112 b and 114 b) may cause a very highthreshold voltage, a very high subthreshold slope, and a strong hotcarrier injection (HCI). The root cause is the high surface dopantconcentration in the FDSOI wells. They are intended as backgates for theSOI devices and need to be highly doped to avoid gate depletion effects.

Furthermore, the formation of source/drain connections causes a degradedsource/channel connection, which cannot be cured by implantingextensions.

In view of the above discussion, it is desirable to provide asemiconductor device and a method improving source/channel connectionand reducing the threshold voltage, as well as the subthreshold slopeand improving HCI.

SUMMARY OF THE DISCLOSURE

The following presents a simplified summary of the disclosure in orderto provide a basic understanding of some aspects of the subject matterthat is described in further detail below. This summary is not anexhaustive overview of the disclosure, nor is it intended to identifykey or critical elements of the subject matter disclosed here. Its solepurpose is to present some concepts in a simplified form as a prelude tothe more detailed description that is discussed later.

Generally, the subject matter disclosed herein is directed tosemiconductor devices and to methods of forming semiconductor devices.In one exemplary embodiment, a method of forming a semiconductor deviceis disclosed that is directed to, among other things, forming a firstwell and a second well in a substrate, wherein the first well is dopedwith dopants of a first conductivity type and the second well is dopedwith dopants of a second conductivity type. The disclosed method alsoincludes forming a third well within the first well, and forming a gatestructure above the substrate, wherein the gate structure partiallyoverlies at least the first and second wells. Additionally, theillustrative method further includes forming a first epi region on thethird well, wherein the first epi region is doped with second dopants ofthe second conductivity type, and forming a drain region that iselectrically coupled to the second well.

Also disclosed herein is an illustrative method of forming asemiconductor device that includes providing a silicon-on-insulator(SOI) substrate having a bulk substrate, a buried insulating materiallayer formed above the bulk substrate, and an active semiconductor layerformed above the buried insulating material layer. The exemplary methodalso includes removing the active semiconductor layer and the buriedinsulating material layer in a first region of the SOI substrate toexpose the bulk substrate in the first region while leaving the activesemiconductor layer and the buried insulating material layer in a secondregion of the SOI substrate. Additionally, the disclosed method furtherincludes forming a first well in the exposed bulk substrate, wherein thefirst well is doped with dopants of a first conductivity type, andforming a second well in the exposed bulk substrate, wherein the secondwell is doped with dopants of a second conductivity type. Furthermore,the illustrative method includes forming a gate structure above theexposed bulk substrate, wherein the gate structure partially overliesthe first and second wells, and forming a first epi region above thefirst well and a second epi region above the second well, wherein thefirst and second epi regions are doped with second dopants of the secondconductivity type.

In a further illustrative embodiment disclosed herein, an exemplarymethod of forming a semiconductor device includes, among other things,forming a trench isolation structure in a bulk substrate of asilicon-on-insulator (SOI) substrate, forming a first well in the bulksubstrate and around a first portion of the trench isolation structure,and forming a second well in the bulk substrate and around a secondportion of the trench isolation structure, wherein the first well isdoped with dopants of a first conductivity type, wherein the second wellis doped with dopants of a second conductivity type, and wherein an edgeof the second well is separated from an edge of the first well by aportion of the bulk substrate. The illustrative method further includesforming a third well within the first well, wherein the third well isdoped with second dopants of the second conductivity type, and whereinan edge of the third well is positioned at a first predetermined spacingfrom the edge of the first well, and forming a gate structure above thesubstrate, wherein the gate structure partially overlies the first well,the second well and the third well, and wherein the gate structureoverlaps the edge of the third well by a second predetermined distance.Furthermore, the disclosed method includes forming a first epi region onthe third well, wherein the first epi region is doped with third dopantsof the second conductivity type, and forming a second epi region on thesecond well, wherein the second epi region is doped with the thirddopants of the second conductivity type, and the second portion of thetrench isolation structure separates the first epi region and the secondepi region.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIGS. 1a-1b schematically illustrate a prior art LDMOSFET semiconductordevice; and

FIGS. 2a-2i schematically illustrate exemplary semiconductor devices inaccordance at various stages of device processing in accordance withsome illustrative embodiments of the present disclosure.

While the subject matter disclosed herein is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the subject matter definedby the appended claims to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the claimed subjectmatter.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of exemplary embodiments. It should be apparent, however,that exemplary embodiments may be practiced without these specificdetails or with an equivalent arrangement. In other instances,well-known structures and devices are shown in block diagram form inorder to avoid unnecessarily obscuring exemplary embodiments. Inaddition, unless or otherwise indicated, all numbers expressingquantities, ratios and numerical properties of ingredients, reactionconditions and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”

Various illustrative embodiments of the present subject matter aredescribed below. In the interest of clarity, not all features of anactual implementation are described in this specification. It will ofcourse be appreciated that in the development of any such actualembodiment, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

The present subject matter will now be described with reference to theattached figures. Various systems, structures and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present disclosure with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present disclosure. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

As used in this description and in the appended claims, the terms“substantial” or “substantially” are intended to conform to the ordinarydictionary definition of that term, meaning “largely but not wholly thatwhich is specified.” As such, no geometrical or mathematical precisionis intended by the use of terms such as “substantially flat,”“substantially perpendicular,” “substantially parallel,” “substantiallycircular,” “substantially elliptical,” “substantially rectangular,”“substantially square,” “substantially aligned,” and/or “substantiallyflush,” and the like. Instead, the terms “substantial” or“substantially” are used in the sense that the described or claimedcomponent or surface configuration, position, or orientation is intendedto be manufactured, positioned, or oriented in such a configuration as atarget. For example, the terms “substantial” or “substantially” shouldbe interpreted to include components and surfaces that are manufactured,positioned, or oriented as close as is reasonably and customarilypracticable within normally accepted tolerances for components of thetype that are described and/or claimed. Furthermore, the use of phrasessuch as “substantially conform” or “substantially conforms” whendescribing the configuration or shape of a particular component orsurface, such as by stating that “the configuration of the componentsubstantially conforms to the configuration of a rectangular prism,”should be interpreted in similar fashion.

Furthermore, it should be understood that, unless otherwise specificallyindicated, any relative positional or directional terms that may be usedin the descriptions set forth below—such as “upper,” “lower,” “above,”“below,” “over,” “under,” “top,” “bottom,” “vertical,” “horizontal,”“lateral,” and the like—have been included so as to provide additionalclarity to the description, and should be construed in light of thatterm's normal and everyday meaning relative to the depiction of thecomponents or elements in the referenced figures. For example, referringto the cross-sectional view of the in-process device depicted in FIG. 2a, it should be understood that the active semiconductor layer 205 isdepicted as being positioned “above” the base substrate 201, and theburied insulating material layer 203 is depicted as being positioned“below” the active semiconductor layer 205 and “above” the basesubstrate 201. Additionally, the “top” or “upper” surface of the activesemiconductor layer 205 as shown in FIG. 2a is depicted as beingsubstantially “horizontally” oriented, and in the cross-sectional viewof FIG. 2c , the shallow trench isolation structures 212 and 214 areshown as extending “below” the “top” or “upper” surface 201US of thebase substrate 201.

Semiconductor devices, such as PMOS and NMOS devices, of the presentdisclosure may concern structures which are fabricated by using advancedtechnologies, i.e., the semiconductor devices may be fabricated bytechnologies applied to approach technology nodes smaller than 100 nm,for example, smaller than 50 nm or smaller than 35 nm, e.g., at 22 nm orbelow. The person skilled in the art will appreciate that, according tothe present disclosure, ground rules smaller or equal to 45 nm, e.g., at22 nm or below, may be imposed. The person skilled in the art willappreciate that the present disclosure proposes capacitor structureshaving minimal length dimensions and/or width dimensions smaller than100 nm, for example, smaller than 50 nm or smaller than 35 nm or smallerthan 22 nm. For example, the present disclosure may provide structuresfabricated by using 45 nm technologies or below, e.g., 22 nm or evenbelow.

The person skilled in the art will appreciate that, although asemiconductor device may be provided by a MOS device, the expression“MOS” does not imply any limitation, i.e., a MOS device is not limitedto a metal-oxide-semiconductor configuration, but may also comprise asemiconductor-oxide-semiconductor configuration and the like.

FIG. 2a schematically illustrates a semiconductor device 200 at a veryearly stage during processing, particularly at a stage where an FDSOIsubstrate wafer is provided for further processing in accordance withfront end of line (FEOL) process flows. The SOI substrate comprises abulk substrate 201, a buried insulating material layer 203 and an activesemiconductor layer 205. With regard to the illustration in FIG. 2a ,the bulk substrate 201 is formed below the active semiconductor layer205, wherein the buried insulating material layer 203 is interposedbetween the bulk substrate 201 and the active semiconductor layer 205.

In accordance with some illustrative embodiments of the presentdisclosure, the active semiconductor layer 205 may comprise one ofsilicon and a silicon-containing material, such as silicon germanium andthe like. The buried insulating material layer 203 may be formed by aninsulating material, such as an oxide material or a nitride material,e.g., silicon oxide, silicon nitride and the like. The bulk substrate201 may comprise silicon or another appropriate semiconductor substrateused as a base substrate in the art.

For example, the active semiconductor layer 205 may have a thickness of20 nm or less, while the buried insulating material layer 203 may have athickness of about 145 nm or, in accordance with advanced techniques,the buried insulating material layer 203 may have a thickness in a rangefrom 10-30 nm. In a special example, the active semiconductor layer 205may have a thickness of 6-10 nm.

In accordance with some illustrative embodiments of the presentdisclosure, the SOI substrate may be provided in accordance with knowntechniques, such as SIMOX techniques or smart-cut processes.

In accordance with some illustrative embodiments of the presentdisclosure, the bulk substrate 201 may be lightly pre-doped with dopantsof a first conductivity type, such as P-type dopants (e.g., boron andthe like), or may be undoped. After a complete reading of the presentdisclosure, the person skilled in the art will appreciate that the bulksubstrate 201, at the present stage during processing, as well as anysubsequent stage, may not be subjected to an implantation processintended to globally dope the entire bulk substrate and the entireprovided wafer (not illustrated). In accordance with some illustrativeembodiments, the bulk substrate 201 may be initially provided with avery light doping or may be undoped.

FIG. 2b schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication, after a provided substrate wafer issubjected to a BULEX sequence at early stages during FEOL processing forlocally removing the active semiconductor layer 205 and the buriedinsulating material layer 203, wherein an upper surface 201US of thebulk substrate 201 is locally exposed.

In accordance with some illustrative embodiments of the presentdisclosure, the BULEX sequence (not illustrated) may comprise forming amasking pattern (not illustrated, however, leaving the portion asillustrated in FIG. 2a exposed) by known lithography techniques, themasking pattern (not illustrated) locally leaving upper surface regionsof the active semiconductor layer 205 exposed to further processing,including one or more subsequent anisotropic etch steps for sequentiallyremoving the active semiconductor layer 205 and the buried insulatingmaterial layer 203 in accordance with the masking pattern (notillustrated), and locally exposing the upper surface of the bulksubstrate 201, including the upper surface region 201US of the bulksubstrate 201 as illustrated in FIG. 2 b.

FIG. 2c schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication, when a process 210 is performed forforming shallow trench isolation (STI) structures 212, 214 in the bulksubstrate 201.

As illustrated in FIG. 2c , an STI region 212 and an STI 214 may beformed in an upper surface region of the bulk substrate 201 by known STIprocesses (e.g., performing anisotropic etching processes for formingtrenches (not illustrated) within an upper surface region of exposedbulk substrate regions, and filling the trenches with an insulatingmaterial, such as an oxide and/or nitride material, thereby forming theSTI regions 212 and 214).

FIG. 2d schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication after an implantation sequence 216 iscompleted, wherein a first well 218 and a second well 222 are formedwithin an upper surface region of the bulk substrate 201.

In accordance with some illustrative embodiments, the implantationsequence 216 may comprise two steps of forming a masking pattern, suchas a first masking pattern M1 covering a portion of the bulk substrate201 around the STI region 214 (as schematically indicated by a brokenline designated with reference numeral M1 in FIG. 2d ), performing animplantation with dopants of a first conductivity type in accordancewith the first masking pattern M1, wherein the first well 218 is formedwithin the bulk substrate 201, removing the masking pattern M1, forminga second masking pattern M2 (as indicated with a dotted broken line inFIG. 2d ), performing an implantation with dopants of a secondconductivity type different from (i.e., opposite to) the firstconductivity type into an upper surface region of the bulk substrate 201in alignment with the masking pattern M2, and removing the maskingpattern M2.

In accordance with some illustrative embodiments of the presentdisclosure, the implantation sequence 216 provides a spacing such thatthe first well 218 and the second well 222 are laterally separated andspaced apart by a material portion 220 of the bulk substrate 201. Inaccordance with some illustrative embodiments of the present disclosure,the material portion 220 may have a substantially lower concentration ofdopants of the first conductivity type when compared to a concentrationof dopants in the first well.

In accordance with some illustrative embodiments, a lateral spacing 224between the first well 218 and the second well 222 may be at least 100nm, such as at least 200 nm or at least 300 nm. After a complete readingof the present disclosure, the person skilled in the art will appreciatethat alignment issues between the first well 218 and the second well 222may be reduced or at least relaxed with increased lateral spacing 224.

The person skilled in the art will appreciate that the first well 218and the second well 222 may be aligned with regard to the STI regions212 and 214, that is, the masking patterns M1 and M2 may be formed inalignment with the STI regions 212 and 214, thereby the STI regions 212and 214 providing a structure for proper positioning the maskingpatterns M1 and M2.

After a complete reading of the present disclosure, the person skilledin the art will appreciate that the STI region 214 is optional and maybe omitted in accordance with alternative embodiments (not illustrated).

In accordance with some illustrative embodiments of the presentdisclosure, the first well 218 may be of a P-type, while the second well222 may be of an N-type. Alternatively, the first well 218 may be of anN-type, while the second well 222 may be of a P-type.

In accordance with some illustrative embodiments of the presentdisclosure, a thermal annealing process may be performed for healingimplantation damages and activating the implanted dopants.

FIG. 2e schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication, when an implantation process 228 isperformed for implanting a third well (see FIG. 2f ) within the firstwell 218.

In accordance with some illustrative embodiments, a masking pattern 226may be formed over the upper surface of the bulk substrate 201, themasking pattern 226 being aligned with regard to the STI region 212. Inparticular, the masking pattern 226 may partially expose an uppersurface of the first well 218, while covering the material portion 220and the second well 222.

In accordance with some illustrative embodiments of the presentdisclosure, the implantation process 228 may comprise implanting dopantsof the second conductivity type into the first well 218 in accordancewith the masking pattern 226 at an implantation energy in a range fromabout 2-10 keV, e.g., in a range from about 4-8 keV, and at animplantation dose in a range from about 1e13/cm² to about 4e13/cm².

FIG. 2f schematically illustrates the semiconductor device 200 after theimplantation process 228 is completed and the further masking pattern226 is removed. Accordingly, a third well 230 is provided within thefirst well 218 in alignment with the STI region 212.

In accordance with some illustrative embodiments of the presentdisclosure, the third well 230 may be formed by doping with dopants of adonor type, such as phosphorous or the like, in case of NLDMOSFETs,while dopants of an acceptor type, e.g., boron or the like, may be usedin case of PLDMOSFETs.

FIG. 2g schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication, after a gate structure 232 partiallyoverlying each of the first well 218, the second well 222, and the thirdwell 230 is formed.

In accordance with some illustrative embodiments, the gate structure 232may comprise a gate stack 234 comprising a gate dielectric and a gateelectrode material, and sidewall spacers 236 covering sidewalls of thegate stack 234. In accordance with some special illustrative examplesherein, the gate structure 232 may be formed in accordance with knownHKMG techniques.

In accordance with some illustrative embodiments of the presentdisclosure, the gate structure 232 may overlap the third well 230 by adistance as indicated by an arrow 237 in FIG. 2g . An amount of theoverlap 237 may be determined in accordance with a target thresholdvoltage to be implemented in the semiconductor device 200.

In accordance with some illustrative embodiments of the presentdisclosure, the gate structure 232 may overlap at least one of the firstwell 218 and the second well 222 by at most 100 nm, such as 58 nm orless.

In accordance with some illustrative embodiments of the presentdisclosure, a target threshold value to be implemented in thesemiconductor device 200 may be designed by appropriately implementing aspacing between an edge E of the third well 230 and an interface Ibetween the first well 218 and the material portion 220. For example, anamount of overlap, e.g., the overlap 237 in FIG. 2g , may be based onthe spacing between the edge E of the third well 230 and the interface Ibetween the first well 218 and the material portion 220.

FIG. 2h schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication, after an epitaxial growth process(not illustrated) is performed, wherein epi regions 242 and 244 aregrown on the third well 230 and the second well 222 in alignment withthe gate structure 232, the STI regions 212 and 214, and a maskingpattern 238 covering a remaining surface of the first well 218 outsidethe third well 230.

In accordance with some illustrative embodiments of the presentdisclosure, the epi regions 242 and 244 may be strongly doped withN-type dopants in case of NLDMOSFETs, or strongly doped with P-typedopants in case of PLDMOSFETs. The doping of the epi regions 242 and 244may be provided when epitaxially growing the epi regions 242 and 244.

The person skilled in the art will appreciate that, in accordance withsome illustrative embodiments of the present disclosure, source anddrain regions may be provided by the epi regions 242 and 244.

FIG. 2i schematically illustrates the semiconductor device 200 at a moreadvanced stage during fabrication, after the masking pattern 238 isremoved and after a masking pattern (not illustrated) covering the epiregions 242 and 244, as well as the gate structure 232, is formed and anepitaxial growth process (not illustrated) is performed, wherein an epiregion 246 is formed.

In accordance with some illustrative embodiments, the epi region 246 maybe laterally spaced apart from the gate structure 232 by a distancegreater than the epi region 242. The epi regions 246 and 242 may beseparated by the STI region 212.

In accordance with some illustrative embodiments of the presentdisclosure, the epi region 246 may be doped with dopants of the firstconductivity type, that is, the epi region 246 and the first well 218may be doped with dopants of the same conductivity type. Accordingly, aback bias to the first well 218 may be provided via the epi region 246.

The person skilled in the art will appreciate that, in accordance withsome illustrative embodiments of the present disclosure, a back biascontact region may be provided by the epi region 246.

Although embodiments above are described as comprising the epi region244, this does not pose any limitation to the present disclosure, andthe person skilled in the art being aware of the present disclosure willappreciate that a silicide region may be provided directly within thesecond well 222 instead of the epi region 244, the silicide regionwithin the second well 222 being aligned with regard to the STI region214.

In accordance with some alternative (and not illustrated) embodiments ofthe present disclosure, formation of the gate structure 232 may compriseforming a field oxide (not illustrated) over the bulk substrate 201,after the implantation sequence 216 in FIG. 2d is completed. Uponlocally thinning the field oxide to a desired thickness for implementinga gate dielectric, the gate structure 232 may be formed, when depositinga gate electrode material on the locally thinned field oxide andsubsequently patterning the field oxide and the deposited gate electrodematerial.

Although the embodiments above show the STI region 214, this does notpose any limitation to the present disclosure and the person skilled inthe art will appreciate that the STI region 214 may be omitted.

The person skilled in the art will appreciate that the process flow asschematically illustrated in FIG. 2i may be continued by applying asilicide module so as to form silicide contact structures forelectrically contacting the epi regions 246, 242, 244, and the gatestack 234.

In accordance with some illustrative embodiments of the presentdisclosure, semiconductor devices may support drain side voltages ofabout 3.3 V or 5 V or higher.

In accordance with some illustrative embodiments that omit the STIregion 214, the deposition of the highly doped epi material on thesecond well 222 may be blocked by an appropriate silicide block liner(not illustrated) which is formed during a process sequence that isperformed in parallel with forming resistor structures on the remainingwafer substrate (not illustrated), the silicide block liner being usedto prevent the silicidation of the substrate surface after the epitaxialgrowth of epi material on the second well 222 is blocked.

In accordance with some illustrative embodiments of the presentdisclosure, semiconductor devices having a gate overlap in the firstwell by 100 nm may be provided. According devices were tested and showeda threshold voltage of about 0.7 V at a drain saturation current inbetween 400 to 450 μA/μm.

In accordance with some illustrative embodiments of the presentdisclosure having a gate overlap of 50 nm, semiconductor devices havinga threshold voltage of about 0.5 V at a drain saturation current ofabout 500 to 550 μA/μm were obtained.

By comparison, conventional semiconductor devices were tested and showedthreshold voltages of higher than 0.8 V at drain saturation currents ofless than 370 μA/μm.

In accordance with some illustrative embodiments of the presentdisclosure, semiconductor devices were obtained that showed asubthreshold slope of improved behavior, that is, a subthreshold slopebecoming smaller with lower threshold voltage and shorter intrinsicchannel length.

In summary, the present disclosure relates to device targeting andperformance of pure slave LDMOSFETs in FDSOI technologies, wherein amethod for fine tuning targeting per litho process is provided. Inaccordance with some illustrative embodiments of the present disclosure,higher drive currents with regard to several LDMOSFET constructions inFDSOI techniques were obtained.

The embodiments of the present disclosure can achieve several technicaleffects and enjoy industrial applicability in any technologies employinghigh voltage transistors, such as automobiles, display electronics,telecommunications, power converters and the like. In the precedingdescription, the present disclosure is described with reference tospecifically exemplary embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the present disclosure asset forth in the claims. The specification and drawings are accordinglyto be regarded as illustrative and not as restrictive. It is understoodthat the present disclosure is capable of using various othercombinations and embodiments and is capable of any changes ormodifications within the scope of the inventive concept as expressedherein.

The particular embodiments disclosed above are illustrative only, as thesubject matter defined by the appended claims may be modified andpracticed in different but equivalent manners apparent to those skilledin the art having the benefit of the teachings herein. For example, someor all of the process steps set forth above may be performed in adifferent order. Furthermore, no limitations are intended to the detailsof construction or design herein shown, other than as described in theclaims below. It is therefore evident that the particular embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the claimed subject matter.Note that the use of terms, such as “first,” “second,” “third” or“fourth” to describe various processes or structures in thisspecification and in the attached claims is only used as a shorthandreference to such steps/structures and does not necessarily imply thatsuch steps/structures are performed/formed in that ordered sequence. Ofcourse, depending upon the exact claim language, an ordered sequence ofsuch processes may or may not be required. Accordingly, the protectionsought herein is as set forth in the claims below.

What is claimed:
 1. A method of forming a semiconductor device, themethod comprising: forming a first well and a second well in asubstrate, wherein said first well is doped with dopants of a firstconductivity type and said second well is doped with dopants of a secondconductivity type; forming a third well within said first well; forminga gate structure above said substrate, said gate structure partiallyoverlying at least said first and second wells; forming a first epiregion on said third well, wherein said first epi region is doped withsecond dopants of said second conductivity type; and forming a drainregion that is electrically coupled to said second well.
 2. The methodof claim 1, wherein forming said third well comprises implanting thirddopants of said second conductivity type into said first well.
 3. Themethod of claim 2, wherein implanting said third dopants into said firstwell comprises implanting said third dopants into an upper surfaceportion of said first well at an implantation energy in a range fromabout 2-10 keV and an implantation dose in a range from about 1e13/cm²to about 4e13/cm².
 4. The method of claim 2, wherein forming said thirdwell comprises forming said third well such that an edge of said thirdwell is positioned at a predetermined spacing from an edge of said firstwell, said spacing being determined based on a target threshold voltageof said semiconductor device.
 5. The method of claim 1, wherein saidfirst epi region is formed by an epitaxial growth sequence that isperformed in alignment with said gate structure.
 6. The method of claim1, wherein said gate structure partially overlies said third well. 7.The method of claim 6, wherein an overlap distance between said gatestructure and an edge of said third well is a predetermined distancebased on a target threshold voltage of said semiconductor device.
 8. Themethod of claim 1, further comprising forming a trench isolationstructure in said substrate prior to forming said first and secondwells, wherein said first and second wells are formed in alignment withsaid trench isolation structure and wherein said trench isolationstructure separates said first epi region and said drain region.
 9. Themethod of claim 1, wherein forming said first and second wells in saidsubstrate comprises forming said first and second wells such that aportion of said substrate separates an edge of said first well from anedge of said second well by at least about 100 nm.
 10. The method ofclaim 1, wherein forming said gate structure comprises forming said gatestructure such that said gate structure overlaps an edge of at least oneof said first and second wells by about 100 nm at most.
 11. The methodof claim 1, wherein an overlap distance between said gate structure andan edge of at least one of said first and second wells is less thanabout 100 nm.
 12. The method of claim 1, wherein forming said drainregion that is electrically coupled to said second well comprisesforming a second epi region on said second well.
 13. A method of forminga semiconductor device, the method comprising: providing asilicon-on-insulator (SOI) substrate, said SOI substrate comprising abulk substrate, a buried insulating material layer formed above saidbulk substrate, and an active semiconductor layer formed above saidburied insulating material layer; removing said active semiconductorlayer and said buried insulating material layer in a first region ofsaid SOI substrate to expose said bulk substrate in said first regionwhile leaving said active semiconductor layer and said buried insulatingmaterial layer in a second region of said SOI substrate; forming a firstwell in said exposed bulk substrate, wherein said first well is dopedwith dopants of a first conductivity type; forming a second well in saidexposed bulk substrate, wherein said second well is doped with dopantsof a second conductivity type; forming a gate structure above saidexposed bulk substrate, said gate structure partially overlying saidfirst and second wells; and forming a first epi region above said firstwell and a second epi region above said second well, wherein said firstand second epi regions are doped with second dopants of said secondconductivity type.
 14. The method of claim 13, further comprisingforming a third well within said first well, wherein said third well isdoped with third dopants of said second conductivity type, wherein saidgate structure partially overlies said third well, and wherein saidfirst epi region is formed on said third well region.
 15. The method ofclaim 14, wherein an overlap distance between said gate structure and anedge of said third well is a predetermined distance based on a targetthreshold voltage of said semiconductor device.
 16. The method of claim14, wherein forming said third well comprises forming said third wellsuch that an edge of said third well is positioned at a predeterminedspacing from an edge of said first well, said spacing being determinedbased on a target threshold voltage of said semiconductor device. 17.The method of claim 13, further comprising forming a trench isolationstructure in said exposed bulk substrate, wherein said first well isformed around a first portion of said trench isolation structure andsaid second well is formed around a second portion of said trenchisolation structure.
 18. The method of claim 17, wherein said secondportion of said trench isolation structure separates said first epiregion and said second epi region.
 19. The method of claim 13, whereinsaid second epi region comprises a drain region that is electricallycoupled to said second well.
 20. A method of forming a semiconductordevice, the method comprising: forming a trench isolation structure in abulk substrate of a silicon-on-insulator (SOI) substrate; forming afirst well in said bulk substrate and around a first portion of saidtrench isolation structure, wherein said first well is doped withdopants of a first conductivity type; forming a second well in said bulksubstrate and around a second portion of said trench isolationstructure, wherein said second well is doped with dopants of a secondconductivity type, and wherein an edge of said second well is separatedfrom an edge of said first well by a portion of said bulk substrate;forming a third well within said first well, wherein said third well isdoped with second dopants of said second conductivity type, and whereinan edge of said third well is positioned at a first predeterminedspacing from said edge of said first well; forming a gate structureabove said substrate, said gate structure partially overlying said firstwell, said second well and said third well, wherein said gate structureoverlaps said edge of said third well by a second predetermineddistance; forming a first epi region on said third well, wherein saidfirst epi region is doped with third dopants of said second conductivitytype; and forming a second epi region on said second well, wherein saidsecond epi region is doped with said third dopants of said secondconductivity type, said second portion of said trench isolationstructure separating said first epi region and said second epi region.